Call indicator



Mmh 3o, 1943.

L. G. SCHIMPF CALL INDICATOR K Rund luy 15,1940

. 3 lSmets-Shut 3.

POLAR/IED NVE/v To@ L G. SCH/MPF A r rom/5V y Patented Mar. 30, 1943CALL INDICATOR Luther G. Schimpf, se. George, N.

Y., assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y.,

a corporation oi' New York Application May 1s, 1940, sei-rs1 No. 335,205

3 Claims.

This invention relates to signaling systems and particularly to numberindicator systems used in telephone systems for making visual display oftelephone numbers.

In certain types of central ofilces an equipment known as a callindicator is employed. 'I'his apm paratus is generally in the form of avisual display annunciator placed before a forwarding operator and isoperated from a distant point.

The object of the present invention is to provide a simple, economicaland eiilcient equipment which `Will be rugged in construction andrequire little maintenance.

A feature of the invention is the use o1' a code indicator wherebynumbers may be indicated by the display of appropriate elements in acode system rather than through the display of arabic numerals.

Another feature is the use of permutation code of a small number ofelements. In the specific embodiment of the present invention hereindisclosed a four-element permutation code based upon an algebraicconception is employed.

Still another feature of the present invention is the use of displayelements which require only transient energization to placethem inoperation. In lthe example given gaseous tubes are used which are red byshort impulses and then remain in operative condition until theircomplete function has been accomplished.

Another feature is the use of display elements which require only atransient energization to prepare them for ultimate operation. By thismeans the various elements of the call indicator are set by serialaction and are later caused to give an indication by a furthersimultaneous action. Specifically the gaseous tubes are weakly energizedand thereafter selectively prepared for final brilliant operationthrough signals sent serially but this rst weak energization is at sucha level that no visible indication is given. Later when the series ofselective signals has bien completely received another operationsimultaneously brings all energized tubes up to such an energized levelthat a visible indication is given.

Another feature of the invention resides in the ;method of operating thegroups of tubes, each group indicating one digit which energizing all ofthe tubes of consists in ilrst, lthe group, second,

maintaining all of" the tubes energized at a low bered at its left-handside'with thev arabic nir-- Vto level, third, selectively andsequentially deenergizing the tubes and fourth, bringing those tubes notdeenergized up to full brilliance.

A further feature of the invention is the use of gaseous tubes which maybe initially ionized in such aJmanner that luminescence is not apparentor at least is unnoticeable. The tubes may be further ionized so thatthey later become noticeably luminescent. According to this feature thetubes are so constructed that in the position from which they are viewedthe electrode from which they are maintained energized after beinginitially ionized, is hidden from view so that even a low levelsustaining ionization does not produce marked luminescence.

Another feature of the. present invention is a physical arrangement ofthe four elements of the permutation code indicators whereby the visibleconnguration of the displayed elements forms part of the code. In thespecific embodiment of the invention herein disclosed a square surfaceis subdivided into four smaller squares 'or quadrants each of whichrepresents one element of the fourelement code whereby the illuminationof these four elemental square surfaces in diiferent combinationscomprise acode.

'I'he drawings consist oi" three sheets, the ilrst showing fouriiguresasfollows:

Fig. 1 is a perspective indication of the placing of a call indicator ona telephone operatorv switchboard shelf. In this gure-the tel" number105712. is shownin code,v y

Fig. 2 is an enlarged cut-awayy of one indicator showing the face withan indication of the fourtubes under, L

Fig. 3 is an indication of the code "e' and s Fig. 4 is a sectionaldesign of the tube,

Figs. 5 and 6 on the other two sheets 'ordrew- Fig.5above!'ig,6;compriseings, when placed with v a circuit diagram for explaining the method ofoperation. f

In Fig. 3 there are` ten squares each one nummetals, 0 to 9 inclusive.In this aure thecede for 0 shows four lighted quadrants. the codeior 1shows three outlet of au ampli t lighted quadrntswiththe uriner;yleft-hand quadrant dark, the codeforeth'efnu-'fl meral 2 shows threelighted quadrants with the upper right-hand quadrant dark, etc. Thiscode is based on an algebraic conception. In Fig. 2

the upper left-hand quadrant is marked 1, the

upper right-hand quadrant is marked 2, the lower left-hand quadrant ismarked 4 and the lower right-hand quadrant should be marked 5. The valueof the digit is the sum of the unlighted quadrants, thus in Fig. 3 withthe upper left-hand quadrant dark the numeral 1 is indicated. Thenumeral 3 is indicated by the unlighted condition of the up'per left andupper right quadrants which have the numeral values land 2, the sum ofwhich is 3. In like manner the numeral '1 is indicated by the unlightedstate of the upper right and lower right quadrants whose numericalvalues are 2 and 5 and whose sum is 7.

Fig. 4 shows an appropriate design of a cold cathode glow lamp. Theglass envelope I is nattened at the top so that it may be placed nearthe display surface under which it is mounted. The cathode 2 isv asemicircular disc as indicated in Fig. 2. The anode is a rod 3 extendingupwardly through the axis of the cylindrical tube to a point near theflattened end surface of the tube. A control anode 4 takes a formsimilar to the cathode 2. There is also a sustaining anode 5 placedbeneath the cathode 2.

In operation a sustaining potential is placed on the sustaining anode 5but this does not ionize the tube. At some later time a potential ismomentarily placed on the control anode 4 which results in theionization of the tube. Thereafter the potential of the sustaining anode5 is sufcient to maintain the tube in an ionized condition but thecathode spot or the cathode glow is so weak that it will not be noticedby one viewing the tube from the top, particularly as the sustaininganode is below the cathode and a greater portion of the discharge willbe to the bottom of the cathode. At a later time the anode 3 isenergized whereupon the top of the tube is lled with a luminescent glow.

One method of operation of this tube, when it forms part of a pluralityof such tubes in a circuit similar to that about to be described, is to,irst, energize the sustaining anode 5, second, to fire the tube throughtransiently energizing the control anode 4, later to selectively quenchthe tubes by transiently shunting the sustaining anode 5 and, lastly, toplace an operating potential on the anode 3 whereby those tubes whichhave been quenched will remain dark and those tubes which have not beenquenched will be brought up to ful luminescence.

In the drawings shown in Figs. 5 and 6 a telephone connection isindicated in a highly schematic manner. A subscribers station 6 isconnected by a line finder indicated by the line terminals 1 and thebrushes 8 to a selector switch 9. When the subscribers line from thesubstation B has been connected through the line finder. a sender I0will be connected to the line and this will receive the numerical digittrains of irnpulses sent from the substation for establishing the wantedconnection. When the designation of the called line has been properlyregistered the line will be extended to a trunk II where,

upon a start relay I2 willbe energized. This relay, through itslower'armature, will place ground on the stepping magnet I3 of theswitch indicated by the wipers I4, I5. IE and I1 and this switch willoperate until the particular trunk has been found whereupon a connectionfrom ground through the upper armature of relay I2 75 will be extendedover the wiper I1, the left-hand armature and back Contact of relay I8,the righthand winding of relay I9 to battery. Relay I9 operates in turncausing the operation of relay I8 and the deenergization of steppingmagnet I3. The battery includingfesistance 20 for operating steppingmagnet I3 is shunted lby the outer left-hand armature of relay I9 sothat the brushes I4 to I1, inclusive, cannot step further. Through itsinner left-hand armature and front contact relay I9 operates relay I8and this relay in turn places a holding ground on the leftliand windingof relay I9 to maintain this latter relay energized for the time being.

Through its outer right-hand armature and front contact relay I9 placesa ground on conductor 2 I leading?- to the holding relay 22. Relay 22operates andperforms several functions as follows: First, through itslower outer armature and front contact relay 22 places a ground on theconductor 23 which has been numbered at various places to indicate itswide distribution.

Secondly, relay 22 through its front contact and.

inner lower armature causes the energization of relay 24. Thirdly,through its upper outer armature and front contact relay 22 placesbattery on conductor 25. It will be noted in Fig. 5 that conductor 25leads to all of the sustaining anodes 5 of the tubes in the hundreds,tens and units columns. Conductor 25 also leads to the control anodes 4in all of the tubes in the ten thousands, stations and thousands tubes.Fourthly, through 'its inner upper armature and front contact relay 22places battery through the back contact and upper armature of relay 24on conductor 2B. It will be noted in Fig. 5 that conductor 26 leadsthrough appropriate resistances to the control anode 4 of all of thetubes in the hundreds, tens and units columns. The energization of thesecontrol units is transient and lasts only until the relay 24, which isslightly slow in operating, has openedithe circuitof conductor 26.However, all of the tubes in the hundreds, tens and units columns havenow been fired and when relay 24 becomes energized they remain ionizedthrough their sustaining anodes 54 but without causing any visibleindication on the key shelf of the operator. The tubes in the thousandscolumn will also likewise be fired through their control anodes 4, sinceeach of the cathodes will nd a circuit to ground on conductor 23 throughthe armatures and contacts of relays 21, 28, 29 and 30. Ionization ofthese tubes, however, willbe low as compared to the nal ionization thatwill occur when their anodes 3 are energized.

The circuit for tube 3l may be traced from the V cathode 2 through theback contact and middle upper armature of relay 21, the upper outerarmature and back contact of relay 30, the upper outer armature and backcontact of relay 29 to ground on conductor 23.

The connection for tube 32 may be traced from its cathode 2 through theoutermost lower armature and baci; contact of relay 21, the upper outerarmature and back contact of relay 29 to ground on conductor 23. Thecircuit for tube 33 maybe traced from its cathode 2 through theA backcontact and outer lower armature of relay 28 and thence through the backcontact and lower armature of relay 29 to ground on conductor 23. The

circuit for tube 34 may be traced from its cathode 2 through the backcontact and inner upper armature of relay 29 and thence through the backcontact and innr lower armature of relay 28 to ground on conductor 23.

The relays 21, 28, 29 and 30 are a translating means for converting thestandard call indicator code for the thousands digit into the standardoperation of call indicator responsive devices for the hundreds, tensand units indicators.

It should be explained that it is standard practice for call indicatorsto be energized by signals in code combinations and that the standardcall indicator code is used herein to operate these cold cathode glowlamps. The standard call indicator code consists in the sending ofpositive and negative impulses. impulses are of a given strength whichis insuflicient to cause the operation of a marginal relay 65 but issuicient to cause the operation of the polarized relay 6I. 'Ihe negativeimpulses are in some cases of this same strength and will thereforecause the energization of the relay 6l but not the energization of themarginal relay 65. In other cases the negative impulses are Yof greaterstrength and will cause the energization of both relays 65 and 6T.pulses will beispoken of as light positive, light negative and heavynegative impulses. y

It will be noted that the extreme left-hand column of tubes are markedten thousands and ods, each digit has four 60 millisecond periods with alight or heavy negative pulse in the second and fourth periods and'either an open or light positive pulse in the rst and third periods.There is no spacing between digits. The code is as follows: Thecharacter represents a heavy negative impulse.

Digits Pulses required periods In lall cases the positive Y ri (img.lOllr. S ,Sm sands tdns 1 2 3 4 units 0 (i 2 l 2O w 4 2 ifi g 3 4 M 1 5Jr f :i j Hereafter these imi i 9 .9 f l l For explaining the action ofthe relays 21 to 39 inclusive, the following table has been prepared:

Period Relays Thousands 1 2 3 4 27 2s 29 ao a1 a2 as l 34 X X X X X X XX X X X X X a X X X X X X X X X X X X X X X .X X X X X stations. Instandard practice one of these tubes will invariably become luminescentto give an appropriate indication. The two lowermost of these tubesmarked 0 and 1 are physically placed in the operators position at theextreme left whereas the other four marked W, R, J and M are placed attheextreme right. In this code that one of these six tubes which becomesluminescent represents the desired indication. In some exchanges In thisthe thousands code has been rearranged innumerical order, the marksindicate the operation of the relays 21 to 30, inclusive, in theirappropriate columns and the operation of tubes 3l to 24, inclusive, intheir appropriate columns.

To explain also the operation of the ten thousands and stations tubesand the hundreds, tens and units tubes the following table has beenprepared:

Period Tubes' eds tens Ten thousands and stations J Relays Digit g 1 2 f3 i 4 1 2 4 5 Digit 0 1 I W J R M 52 53 70 7l 0 X X X X 0 X 1.. X X 1 X2 X X X v X X 3 e X X R X X X 4. X X X J X X 5. X X X M X X X X 7. X X 8X 9 X X g there may be over 9,999 lines, that is, there may 1 Thenegative pulses are stepping chain which each used to control thecomprises two relays for aolumn of tubes shown in Fig. 5, for instance,relays 36 and 8B associated with the ten thousands and stations tubes,relays 37 and se associated with the thousands tubes, relays 39 and t@associated with the hundreds tubes, relays 4l and 42 associated with thetens tubes and re-, lays d3 and $4 associated with the units tubes.`

These pulses last for about 60 4 asiento There is a well-knowncombination of relays energizingpircuitlfor relay4 .willbe opened but asthe W and Z relay combination. Relay 45 is a circuit may .now -be-tracedfrom battery, vthe f i the W relay and relay 43 is the Zrelay.v In thelower windingol .relay 43, the winding of relay example about to begiven the telephone number 45,- the winding of relay I3, the iront contobe sent by the sender il into this circuit will- .5 tactand lowerarmature of relay `45 to ground consist of the designation R1057 and thecomi ontheconductor 23 so that relay 43 now becomes plete code of pulseswill be as follows: operated.

1234-1:s ijrgzsri234.12.34

n i 1 c l i s 1 It will be noted in this code thateach'desig The nextimpulse is a light negative impulse nation has 'in it two negativespulses. 'Upon the resulting in the operation of relay G1 alone. Reflrstnegativeimpulse the' Wi relay here desigf lay l1 now connects groundfrom conductor 23 mated 45 `will be energized. At the end of thislthrough the outermost lower armature and back impulse the Z relaydesignated 43 will become 2 0 contact of relay 43, the lower armatureand front energized. Upon the arrival ofthe next negtive' v u Contact ofrelay 4I to the conductor joining the impulse 'the W relay will becomedeenergiaed lower` winding of relay 4o and the winding of relay and atthe end of this negative impulse the Z r'e 4 5. Relay 45 and the upperwinding of relay 45 lay will become deenergised. Thus, through eachfarethus shunted resulting in the deenergization 'designation the W and Zrelays will operate' in 25 of relay 45 but the holding of relay 43. Atthe a cycle including allposrxible` combinations of v end of thisimpulse when relay 81 returns to the energized and deenergized states.By the acthe position shown, relay 46 becomesl deenertion of the Z relayin each ease the chain relays v sized. for the digit Just registeredwill be operated-toe` Thus relays 52 and 53 will have been operatedextendthe chainto the next digit. 30 by the code tor station letter R.-Thereupon a now to the chain of operations're. i 1 circuit may be tracedfrom ground on conductor sulting rin tile movement of the brushes v|4150I1 1l 'through the outer upper armature and front inclusive to theseized trunk le'vel and the consccontact of relay 53, the lower armatureand front quentoperation of relays I! and 24, it will be L: contact ofrelay l2, conductor 54 in the cathode noted that upon-.the energization.0f relay 2l- 35- 3 of tube 55. Through the potential on thecongroundgis extended over conductor 41 to thewindki ductor 35, tube l5will be ionized. at a 'low level ing o! 43. Relay." connects the trunkcone @ready for complete ionization through its anode ductorsiithroughthe wipers i4 and il to con-v` -lat a later time as will be hereinafterexplained. ductors la and Il, respectively. Conductor 43,l lt has beenshown above 'howgjthe W relay 45 maybemeed through the-middleimpersnna'- 40. become; enmised at the' beginning of dthe mst .tureandback contact oiv relay 43 through fnega'tive impulse, how the Zrelaylt'becomes enwinding of-marginilrelayjllythe winding of theV at thevending of the ilrst negative imllglit positive relay 35. the winding.ot iight negapulse, how the W relay 4l becomes deenergized attive'relayfll, back contact and inner upper arma-` beginning of thesecond negative impulse and tureofrelay u to conductor I0 and thisbridged? i5-now the zl relay u becomes deenerglzed at the across thetrunk comprises a signal to the sender end oi the second negativeimpulse. It should I0 whereby-the senderv is caused to begin its'A nowbe noted that thepairs of relays 35, 36, etc. sending of thecallindicator code impulses above .follow the action oi' the W and Z relays.Thus, set out.` 1 fat. the end of vthe iirst negative impulse when theUpon the i'rlval'ofthe rst impl-118e. which isno Z relay 45 becomesenergized a connection is a light positive impulse, relay 33 will becomeenextended from ground on conductor 23 through ergized. Thereupon groundfrom conductor v23 v the outer upper amature of relay 46, the lnnr willbe extended over, the upper armature and l upper armature and backcontact of relay 35,

f baci: contact of relay 4l and thence through winding of relay 3i tobattery. Thus, relay 36 `upper outer armature land back contact ot relaysc becomesenergized simultaneously with the ener- 33 to the winding ofrelay 52. l-'toiay l! giaaticn of the Z relay 4l.' Relay 35 now connectsthrough itsupper winding to groundonoonductor' ground from conductor 23through its inner lower 23. Upon the secondyinpulse. which is armatureand front contact to the winding oi' negative, both relays "..and l1will become 35 but since the other terminal of relay 35 ergized. RelayI1 'will ground from is'jalso connected to ground this connection isinductor I3 over the lower outermost armatx're'gr' ljeilective forv thetime being. When the Z relay ot relay 43 and its back contact through{.Lbemmes deenergized at the ending of the seoer armature andfbackcontact of relay ,lndl-v ond negative impulse this short circuitl aboutvthe ing of relay u, lower winding of relsgslto bet- ..n rindin of relayl5 disappears and relay 35 new tery. Relay 45 operates in this but the`energized in series with relay 35. In current flowing through thelowerwin'gling o! gV this manner the control of relays 3 5, 33 and 31lay 46 alone is insufncient tocause operadon' g.; @istralsierred fromtheten thousandsv and staoi this latter relay ,46. Relay will extend'`tions indicators tothe thousands indicators. ground from conductor n,'through 4its armature 'l Upon the energization of relay 35 a connectionand front contact,l the Aarmature andwyis extended from ground, ltheinner upper armaback contact of relay "fthe outerv lower arma` I .jtureand iront contact of relay 35 through the ture and. back contactoi.relay '34,lower winding.. middle and lower amature and back contactof of relay 53 to battery.v Relay 53 becomes oper- Vj'frelay 43 to thewinding oi relay 55. Relay 56 ated and locks to ground on conductor 23.`Einattracting its amature the circuit for At the end of this negativeimpulse the original '16 'relays Il and 53 so that neither of theserelays will become energized until after the units regis-4 tration hasbeen made. s ,l

According to the example given the telephone number to be written up is1057 station R:` The station designation R has been written upandnegative impulse relay 61 becomes lenergizedwhereupon ground isextended fr'om'thev armature and contact of relay 61 through theoutermost lower armature and back Contact of relay 43, the lower amatureand back contact of relay 46, the winding'of relay 45, the lower windingof relay 46 to battery whereupon the W relay 45 becomes energized.' Atthe end of this impulse the relay 46 becomes energized asr herenbeforeldescribed. At this time also relay 38 becomes energized in a mannersimilar to that heretofore described. Upony the next impulse which is aheavy negative impulse, the marginal relay 65 becomes energizedwhereupon a connection is extended from ground on conductor 23 throughthe armature and front contact of relay 65, the' inner upper armatureand rr`front contact of relay v46, lower'armature and front'contact ofrelay 35,-- the lower armature and back contactof relay 31, the winding.of relay 30 to battery. Relay 30 becomes energized in this circuit andlocks itself to ground on conductor 23. vAt the e'nd of this heavynegative impulse'relay 46 becomesdeenergized resulting in theenergization of relay 31 thus ad,-

tube. The second heavy negative impulse will likewise result in thequenching oi' tube 13. Tube 12 is vthe No. 2 tube'and tube 13 is the No.5 tube,

vtheir algebraic sum is.'1 so that' through their failure to lightbrilliantly a -moment later units indicator will indicate the digit 7.

Two types of senders lll can be connected to this circuit. Some senderssend a heavy positive pulse after' the units digit has been transmittedwhile other senders do not send the heavy positive pulse. ASince themostgeneral caseis the condition where the heavy pulse may or may not besentv the circuit is designed to meetthis rethe cuiIement.' Relay 43operates at the termination of the last unit, pulse and locks in serieswith l relay 44. These relays operated open the leads vancing the chainto the hundreds group of tubes.

Through the energization of relay the heretofore described connection ofground to the cath# ode 2 of tube 3l will be opened so that tube 3l isthus selectively deenergized.

The next series of impulses to be registered on the hundreds indicatorconsists of two light negative impulses representing the digit 0. Inaccordance with these impulses not one of the tubes in the hundredscolumn will be disturbed but the two negative impulses will result inthe energizavtion irst of relay 40 and then of relay 38 thus advancingthe chain to the tens column. In this case the code is presented by alight negative impulse followed by a heavy negative impulse. At the endof the light negative impulse, relay 42 will become energized.Thereafter the heavy negative impulse will result in the connection ofground from conductor 23 through the armature and front contact of relay65, the inner upper armature and front contact ofrelay 46, the lowerarmature and front contact of relay 35, the lower armature and frontcontact of relay 31, the lower armature and front contact of relay 39,the lower armature and back contact of relay 4l to the sustaining anode5 of tube 59. This momentary ground on the sustaining anode 5` willshunt the potential connection thereto through the resistancesufficiently to quench the tube 59. Tube 59 represents the No. 5 tubeand through its failure to light brilliantly at a later period willindicate the digit 5.

At the end of the heavy negative impulse re,-

I lay 4l becomes energized and extends the chain 4to the units register.The units code consists of taining anode 5 of tube 12 thus quenchingthis 75 to the units digit tubes and vrelay 44 connects ground to acontact of relay 56. Relay 56, as before described, was operated uponthe operation of relay 36 through the middle lower armature and backcontact lof relay 43 but now that relay 43 has become energized relay 56returns to normal.

" The operation of relay 43 reverses the tip and ring leads to the lightnegative relay 61 and renders inoperative the light positive andmarginal relays 66 and 65. Thus, relay61 is connected in acircuitwhereby it will respond to a positive impulse'. the switch wiper I4'through the front 'contact n and left-hand armature oi' relay 46, themiddle relay becomes deenergized. The relay, however, vis slow torelease so that if the sender l0 is equipped to send a heavy positiveimpulse at the end of the units series this may operate relay 61 beforerelay 56 has made its back contact. In this case relay 61 connectsground through the outermost lower amature and front contact o1' relay43 to the winding of relay 56.V If the panel sender is not equipped tosend this positive impulse then the energization of relay 58 awaits thecomplete release of' relay 56. At this time ground is connected throughthe front contact and inner lower armature of relay 54 and the armatureand back contact of relay 56 through the windings of relays 51 and 5l inseries. Relay 58 through its outer upper armature connects battery'toconductor 6| which leads to the anodes of all of the tubes and bringsthose which are still ionized up to full brilliance whereby the numberof the called telephone line is displayed before the operatorhavingunder her control the plug 22.

In the first assumed case where the operation oi' relay 58 is controlledby a. heavy positive impulse it should be noted that the operation ofrelay 58 connects ground from the innermost lower armature and frontcontact of relay 44 to the winding of relay 51 but relay 51 does notoperate as long as this positive impulse persists.

- As soon as it ceases, however, relay 51 becomes energized in serieswith relay 58. Upon the energization of relay 51 a ground is connectedthrough the armature and front contact of relay 51 to conductor 83-whichmay be traced through The circuit may be traced from the wiper I8 to theupper winding of relay 8l. Relay 84, thereupon, becomes energized andextends the trunk conductors through to the winding of relay 68. RelayG8 maintains relay M energized thereafter. Relay Il Acuts oi'f thestarting relay l2.

When the operator completes the connection and has no longer need toView the call indicator she may release this apparatus by depressing key69 which opens the holding ground for relay I8 and since at this timerelay I2 has become deenergized, relay I9 will release. When relay Ilreleases the ground for holding relay 22 is re moved from conductor 2|and the circuit is returned to normal.

What is claimed is:

l. An indicating device comprising a gaseous discharge device in atubular envelope having a substantially ilat circular end portion, saiddevice having an anode and cathode so constructed and arranged that thedischarge therebetween will illuminate saidA end portion of saidenvelope, a cont-rol anode visible through said end portion of saidenvelope and a. sustaining anode at a point remote from said end portionof said envelope and arranged behind said cathode whereby any glowdischarge between said sustaining anode and said cathode is invisiblethrough said end portion of said envelope.

2. A gas discharge tube for use as a signaling means comprising a bulbcontaining an inert gas, a press within the bulb, a substantially iiatcircular end portion of said bulb through which a glow discharge may beviewed,v a substantially fiat semicircular cathode supported by saidpress, a substantially ilat semicircular control anode supported by saidpress, said semicircular elements being in a plane parallel to said atend portion of said bulb, an axially located anode supported by saidpress and extending to a point substantially midway between the plane ofsaid semicircular elements and said ilat end portion oi' said bulbwhereby a glow discharge on the face oi' said cathode visible throughsaid dat end portion may b e produced, and a sustaining anode supportedby said press and hidden from view behind said cathode.

3. A signaling device consisting of a bank of visible display indicatorseach consisting of a tube constructed vaccording te claim 1, a circuitarrangement responsive to seizure of said device for simultaneouslyapplying an operating potential between the said sustaining anode andthe said cathode of all of said tubes, transiently operated meansfurther responsive to seizure of said device ior applying a strikingpotential to the said controlA anodes of all of ysaid tubes, meansresponsive to coded impulses for selectively appiying a quenchingpotential to said sustaining anodes and means responsive to thecompletion of a coded train of impulses for applying an operatingpotential between the said anode and the said cathode of all of saidtubes, whereby the unquenched tubes of .said bank are caused to visiblyglow. Y

LUTHER G. SCHIMPF.

